margaret thatcher died of a stroke last month at age 87. >>> more than 100 federal, state and local investigators are scouring a 12-block stretch around boylston street for clues to who was responsible for the bombing. mark mazetti is a correspondent for "new york times," and author of "the way of the knife." about the secret drone war. first of all, mark, congratulations on the book. >> thank you very much. >> rave reviews and extraordinary reporting here. first about boston and what we know. there's a great deal of interest about whether this could have been foreign or domestic. we don't know that yet. this is a very common type of homemade incendiary device. >> pete williams gave the latest on where the federal authorities are zeroing in on suspects. the big sort of story yesterday was the construction of the bombs and whether speculatively, the bombers could have taken any inspiration from an online magazine only al qaeda in the arabian peninsula. even if that was the case, it wouldn't tell you if it was foreign or domestic. the point of the magazine was to tell everyone how to go do somethin